[alsa-devel] fsl_ssi.c: Roberto's problem: ssi hangs after some number of samples

[Caleb Crome]

On Thu, Nov 5, 2015 at 3:28 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>
>
> On 11/06/2015 12:21 AM, Caleb Crome wrote:
>> On Thu, Nov 5, 2015 at 3:01 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>
>>> On 11/05/2015 11:49 PM, Caleb Crome wrote:
>>>> On Thu, Nov 5, 2015 at 2:40 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>> On 11/05/2015 11:25 PM, Caleb Crome wrote:
>>>>>> On Thu, Nov 5, 2015 at 2:08 PM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>> On 11/05/2015 10:34 PM, Caleb Crome wrote:
>>>>>>>> On Thu, Nov 5, 2015 at 3:48 AM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>>>> On 11/05/2015 12:30 PM, Fabio Estevam wrote:
>>>>>>>>>> On Thu, Nov 5, 2015 at 8:03 AM, Roberto Fichera <kernel at tekno-soft.it> wrote:
>>>>>>>>>>
>>>>>>>>>>> Following your suggestion, I've increased the buffer size to 2K and set the period to fifo_length - 2 (13),
>>>>>>>>>>> with that I'm now running substantially smooth except 3 EVTERR on RX DMA over 4 million of interrupts.
>>>>>>>>>>>
>>>>>>>>>>> Thanks Nicolin! I'm quite happy now!
>>>>>>>>>> That's good progress, Roberto.
>>>>>>>>>>
>>>>>>>>>> It would be nice if you and Caleb could post the patches to the mailing list.
>>>>>>>>>>
>>>>>>>> Yes, when I get something quite solid, I'd like to submit it all to
>>>>>>>> the list, and hope to get it into the kernel so nobody else has to go
>>>>>>>> through this pain again.
>>>>>>>>
>>>>>>>>> Indeed! Now the TDM is stable, I've also found the reason of the EVTERRs, which was related to some stale
>>>>>>>>> code I've used to enable and disable both RDMAE and TDMAE bits to try to reset the transfers.
>>>>>>>>> Once removed that code everything is looks ok now.
>>>>>>>>>
>>>>>>>>> Regarding patches, well, from my side there isn't nothing special compared to the original fsl_ssi.c code.
>>>>>>>>> I'm basically running against a very skinny fsl_ssi.c version, I've just setup a bit larger DMA buffer, from
>>>>>>>>> 16bytes to 2K, and now reduced the DMA period to 8 because I'm mostly comfortable with that size to simplify
>>>>>>>>> sampling exchange against DAHDI subsystem within my DMA callbacks.
>>>>>>>>>
>>>>>>>>> In a few words, my problem was related due to a DMA buffer too small.
>>>>>>>>>
>>>>>>>>> What eventually might be interesting to have is the INTRMASK and EVTERR DMA setting to trigger DMA
>>>>>>>>> related errors, but I guess this need to be discussed elsewhere.
>>>>>>>> I have implemented roberto's patch on the 4.2 kernel, and I get a huge
>>>>>>>> number of EVTERR interrupts.  Something like 7200/second at 16kHz
>>>>>>>> sample rate.  But strangely, the audio seems to be correct.
>>>>>>> I've notice that clearing the EVTERR bit seems restarting the given SDMA.
>>>>>>>
>>>>>>>> My patch is slightly different in that it just enables EVTERR for all
>>>>>>>> channels, not just for the SSI.  Might as well see if there are any
>>>>>>>> other problems.
>>>>>>> Oh yes! This will overload the SDMA isr.
>>>>>> It didn't seem to.  There didn't seem to be any other DMA happening in
>>>>>> my system, definitely none that made the EVTRR trigger.  However, I
>>>>>> changed it back to the way you had it.  No differences, still got a
>>>>>> TON of EVTERRs.
>>>>> This might be related to SDMA request when another is pending.
>>>>>
>>>>>>> How bigger is your audio buffer?
>>>>>>> In your case I guess you will need something like 16KHz * 16 channels *
>>>>>>> 2 bytes (16bits) = 512K minimum.
>>>>>>> I would try to start from 1MB or maybe more.
>>>>>> That's 2 seconds of audio!  We definitely need less buffering than
>>>>>> that.    We pretty much need a latency of 100ms, worst case, or 1600
>>>>>> frames, or 51,200 bytes.
>>>>> I haven't checked in detail how the DAI buffering is working, but likely
>>>>> the samples are passed not in buffer size chunks but instead with less
>>>>> granularity. Having a large buffer gives more chance to the SSI to not
>>>>> overlap DMA requests, hence no more EVTERRs.
>>>>>
>>>>> I would give it a try.
>>>>>> I did change the max buffer size to 1MB though, but I'm not sure how
>>>>>> much is actually being used.
>>>>> I guess it's 64K, look for IMX_SSI_DMABUF_SIZE.
>>>>>
>>>>>
>>>> Exactly, I changed that to 1024*1024, but still I don't get zero
>>>> EVTERRs, even when I set my periods long and number of periods high.
>>> They decreased?
>>>
>> the big win was going to dual fifo, but they're still there at
>> something like 17/second.
>
> What about your current fifo_depth? Are you using the full length?
>

Do you mean in the SSI watermark, or some other FIFO depth?

I'm currently operating at watermark = 6 & DMA maxburst of 12 (dual fifo mode).

That's the best performing so far.

-Caleb